Credits

What will you get?

You will have a Debian Squeeze userland and the stock Buffalo kernel of your already installed firmware.
So it is not a full replacement of Buffalos firmware, but mostly. ;-)
To have a "complete" Debian Squeeze installation one would need to replace the kernel also. But user benoqkuke hasn't managed to build his own kernel (newer than 2.6.31) yet. So stay tuned, if you want to have a more recent kernel also.

What you need beforehand

You have to be able to use the root account on the NAS.
You can use [2] CHL-v2/XHL 1.37 Mod 1 firmware to do that.

Debootstrap

You need to install debootstrap.
To be able to do this, you need to download the package.
Log on as user root on your box and and execute this:

Move hddrootfs.buffalo.updated to a folder that you can access from you computer.
Download empty initrd from [3] to your lsupdater folder.
Copy hddrootfs.buffalo.updated to your lsupdater folder.
Remove initrd.img and hddrootfs.img from your lsupdater folder. (If you use 1.37mod1 kernel you just need to replace them when you copy these file)
Add debug options to lsupdate: open LSUpdater.ini and check that it look like that :